Scientists have determined that a number of human activities may be contributing to global warming by adding excessive amounts of greenhouse gases, such as carbon dioxide, to the atmosphere. Carbon dioxide traps heat that normally would exit into outer space. While many greenhouse gases occur naturally and are needed to create the greenhouse effect that keeps the Earth warm enough to support life, human use of fossil fuels could be a source of excess greenhouse gases. By driving cars, using electricity from coal-fired power plants, and heating our homes with oil or natural gas, humans release carbon dioxide and other heat-trapping gases into the atmosphere. Deforestation is another significant source of greenhouse gases, because fewer trees mean less carbon dioxide conversion to oxygen.
During the 150 years of the industrial age, the atmospheric concentration of carbon dioxide has increased by 31 percent. One way to reverse this trend is to introduce a system that can split oxides of carbon into carbon and oxygen. One approach is to use a photocatalyst. However, most photocatalysts work in the UV region and are inefficient or do not absorb visible light.